Question

This is one for all you security gurus out there.

I have a SQL Server 2005 database with a database master key, which is encrypted with a very strong password using the server key, which in turn is encrypted using the service account credentials in the Windows Data Protection layer.

I have a certificate which is encrypted using the database master key.

I have a symmetric key using AES256 which is encrypted using the certificate, and I am using the symmetric key to encrypt and decrypt confidential fields in the database.

What does someone need to crack the encrypted fields in the database? My only assumption is that brute force can’t be employed due to the strength of the symmetric encryption algorithm, and the symmetric key itself is protected by 4 additional layers of encryption:

Windows DPAPI -> Server -> Database -> Certificate -> Symmetric Key

which seems pretty tight to me.

Let’s not include the obvious answer of ‘get the system administrator’s username and password by drugging and sleeping with him’, which is definitely relevant but not what I’m after.

Answer 1

Here is a potential attack. It assumes you already have a way to run arbitrary code as the service account. For example, you might exercise a remote code execution bug to get. Having done so, it is relatively trivial to use DPAPI to get the server key. Having done that, you can get the master database key, although you’d need some brute force method to break the password.

It sounds like it would be pretty difficult to do, depending on the strength of the password maybe impossible. Is the service account low or high privileged? If it is an admin account, you could maybe use that (assuming it was broken) to install a keylogger to get the password.